The idea of blocking a firing pin to prevent the discharge of a reciprocating-bolt firearm when the bolt is in an unlocked position is not new. U.S. Pat. No. 2,645,873 to L. R. Crittendon shows a slide-actuated firearm which has a reciprocating bolt that is locked to the barrel by a tilting locking block, as the bolt is closed by forward movement of a slide block. The locking block has buttresses at its rear end, which, in its unlocked, downwardly-tilted position, block an enlarged head on the firing pin to prevent the firing pin from protruding from the bolt face. The blockage is removed as the locking block is tilted upwardly into engagement with a locking recess in a barrel extension.
This device is satisfactory except in cases where the firing pin is bent enough to jam in the bolt in its forward position protruding from the bolt face; or where the firing pin spring is broken. In these circumstances, the firing pin is not withdrawn by the firing pin spring and the buttresses on the locking block are cramped down against the enlarged head of the firing pin as the opening movement of the bolt tilts the locking block down from its locked position. This may jam the mechanism, or actually break the firing pin. Another potential difficulty is that since the tilting motion of the block and its buttresses is necessarily very short, the blocking and retracting action depends on the maintenance of close tolerances, and may be adversely affected by wear or distortion of the parts.
Another type of firing pin block, applicable to a recoiling-barrel actuated reciprocating-bolt action, is shown in U.S. Pat. No. 2,570,772 to L. R. Crittendon. Here, a tilting locking block is pivotally connected to the slide block, and is urged forwardly by an action spring against a bolt surface, which normally wedges the locking block upwardly into locking engagement with a recess in the barrel extension. When the barrel moves rearwardly from its battery position after firing, however, it cams the locking block down out of the recess. This wedges the locking block against the bolt surface so as to displace the bolt slightly forward relative to the slide block, to a position in which any forward movement of the firing pin is blocked by the slide block before the firing pin can protrude from the bolt face. This blockage is maintained until the barrel is moved forward to battery position and the locking block is re-engaged in the barrel extension recess.